1. Field of the Invention
The present invention is related to a positioning device for a prestressing magnet of a spindle motor and more particularly to the positioning device having an adjustable positioning member to thereby adjust a position of the prestressing magnet for balancing the spindle motor during rotation.
2. Description of the Related Art
Referring to FIG. 1, a conventional spindle motor 1 comprises a stator 10, a prestressing magnet 11, a bearing 12, a rotor 20, and a metal casing 21. The prestressing magnet 11 is attached to the stator 10 by adhesive while the bearing 12 is inserted into the rotor 20. A shaft 22 of the rotor 20 extends through the bearing 12 of the stator 10 to form the spindle motor 1. Axially aligned with the metal casing 21 of the rotor 20, the prestressing magnet 11 provides an axial magnet force to thereby cause balanced rotation of the rotor 20. Consequently, a gap width (a) formed between the prestressing magnet 11 and the metal casing 21 is inversely proportional to the magnetic force therebetween.
Referring to FIG. 2, another conventional spindle motor 1 comprises a stator 10, a prestressing magnet 11, a bearing 12, a rotor 20, and a metal casing 21. Formed with a neck portion 121 at its end, the bearing 12 is inserted into the stator 10. The prestressing magnet 11 is attached to the neck portion 121 of the bearing 12 to form a unit. A shaft 22 of the rotor 20 extends through the bearing 12 of the stator 10 to form the spindle motor 1. Axially aligned with the metal casing 21 of the rotor 20, the prestressing magnet 11 provides an axial magnetic force to thereby maintain the rotor 20 in balanced rotation. Consequently, a gap width (axe2x80x2) formed between the prestressing magnet 11 and the metal casing 21 is inversely proportional to the magnetic force therebetween.
Because the gap widths (a and axe2x80x2) formed between the prestressing magnet 11 and the metal casing 21 are fixed, the axially magnetic force therebetween cannot be adjustable. In other words, the magnetic force generated between the prestressing magnet 11 and the metal casing 21 cannot be increased or decreased according to product features. In order to adjust the magnetic force, an appropriate position of the prestressing magnet 11 on the stator 10 must be changed.
The present invention intends to provide a positioning device for a prestressing magnet of a spindle motor having an adjustable positioning member adapted to adjust a distance with respect to a rotor in such a way to mitigate and overcome the above problem.
The primary objective of this invention is to provide a positioning device for a prestressing magnet of a spindle motor having an adjustable positioning member fittingly combined with a stator to thereby adjust a distance of a position of the prestressing magnet with respect to a rotor.
The positioning device for a prestressing magnet of a spindle motor in accordance with the present invention mainly comprises a stator, a positioning member, a prestressing magnet, a rotor and a metal casing. Combined with the prestressing magnet, the positioning member is fittingly secured to a predetermined position on the stator while the metal casing is secured to the rotor. After combining the stator with the rotor, the prestressing magnet is axially aligned with the metal casing. An axial magnetic force generated between the prestressing magnet and the metal casing maintains balanced rotation of the rotor.
Another aspect of the present invention is that the positioning member is fittingly pressed to secure to a predetermined positioned formed on an outer circumference of a neck portion of a bearing or the stator.
Another aspect of the present invention is that the positioning member is fittingly pressed to secure to a predetermined position formed on an outer circumference of an axial tube.